Both at home and at restaurants it is conventional for hot food to be served on a plate which has been warmed. There are various techniques for warming plates in the kitchen, including placing them in the oven, under a heat lamp, or in contact with an electrical resistance heating blanket. Typical of such resistance heating plate warmers, for example, is the device of U.S. Pat. No. 3,140,389.
While these techniques for maintaining food at an elevated temperature during consumption are effective at the start of a meal, they are of little assistance and relatively ineffective after only a short period of time. Convection and conduction heat transfer soon cool the mass of the serving dish or plate, as well as the food, with the result that the food temperature rapidly drops to ambient temperature during the course of a meal.
Several food warming devices have been developed which provide a constant source of heat for the food throughout the process of consuming the same. Typical of such apparatus are the food warmers of U.S. Pat. Nos. 3,586,824; 3,784,787; 4,493,978; and 4,523,083.
U.S. Pat. No. 3,586,824 discloses a food warming apparatus in which a heating element is mounted on a support surface or counter and a thermally conductive metallic plate is positioned immediately above and biased away from the heating element. When the user positions a dinner plate carrying food on the metal plate, the metal plate is displaced downwardly by the weight of the dinner plate and food against the heating element, and a switch is actuated to turn on the heating element. The heating element then warms the metallic plate, which in turn warms the plate on which the user's food is supported.
While this approach can be effective to warm food, it also inherently has certain safety problems. More particularly, such a plate warming device requires that the metallic plate be heated to a substantial temperature in order to transfer sufficient heat from the heating element to the metallic plate, from the metallic plate to the dinner plate and thereafter to the food. Moreover, when the plate on which the food was positioned is removed, the metallic plate moves away from the heating element, but it will remain at a substantial elevated temperature posing a burn hazard. Additionally, when the metallic heat transfer plate is in the up position, it is difficult to clean the counter or surface in which the plate warmer is positioned, and there is a likelihood that cleaning liquids will migrate into the area of the electrical components where corrosion, shorting or electrical shock can result.
The food heating and cooking apparatus of U.S. Pat. No. 3,784,787 employs a specially designed tray which receives mating casseroles. Each casserole is provided with an electrical heating element, which includes electrical terminals that are indexed with respect to terminals on the tray. Positioning of the casserole in the tray completes an electrically conductive circuit permitting heating. The system, however, is primarily designed to cook food inside a surrounding container and is not well suited for consumption of the food while positioned in the casserole on the tray. Moreover, such a plate warming system would not be well suited for use at a restaurant or coffee shop counter or table where liquids on the counter or table could cause shorting between the exposed terminals in the tray.
U.S. Pat. No. 4,493,978 discloses a serving dish which similarly is placed upon two exposed electrical contacts on a tray. The tray is constructed such that precise positioning of the serving dish on the contacts is not required in order to complete the electrical circuit, but the problem of spilled fluids shorting between the contacts on the tray still exists. Additionally, the special serving dish is constructed with metallic plates which are in close thermal contact with the heating element carried by the serving dish. When the serving dish is picked up off the tray, therefore, there is a burn hazard in connection with such plates.
A beverage warmer for heating beverages while in a cup or container is disclosed in U.S. Pat. No. 4,523,083. The beverage warming device has an electrical heating coil which is mounted on a tray or support surface on which the cup is placed. The device is switched on and off by a magnet carried by the cup and a reed switch mounted on the tray so that when the cup is placed in proximity to the reed switch, the heating coil is switched on. This approach, however, again results in a very hot surface when the cup or food container is removed from the surface which performs the heating.
It is desirable to be able to automatically control the temperature to which food is heated by food warming apparatus. U.S. Pat. Nos. 4,307,287 and 4,399,351 show typical food cooking apparatus which incorporate temperature control means which are mounted in contact with the bottom surface of the cooking appliance. Such controllers typically employ an intermittently operating switch which turns the electrical current on and off so as to maintain the appliance within a predetermined temperature range.
Accordingly, it is an object of the present invention to provide an automatic food warming device suitable for use in restaurants, coffee shops and the home by relatively inattentive users which food warmer is effective in maintaining the food at an elevated temperature during consumption and yet is very safe and trouble free in its operation.
Another object of the present invention is to provide a food warming device which may be easily cleaned with water or other conventional liquid cleaning agents without corroding the electrical components or creating a significant shock or short circuit hazard.
A further object of the present invention is to provide an electrical food warming device which will maintain food on a user's plate at an elevated temperature without posing a burn hazard to the user or to the person serving and removing the plates.
Another object of the present invention is to provide an electrical food warming device which can be used to maintain the food at an elevated temperature both while it is waiting to be served and while the user is consuming the food.
Still a further object of the present invention is to provide a food warming apparatus which can easily be retrofit into existing counters and table tops, is inexpensive to construct and operate, is very durable and relatively maintenance free, and automatically maintains food at a predetermined temperature.
The food warming device of the present invention has other objects and features of advantage which will become more apparent from and are set forth in more detail in the following description of the Best Mode of Carrying out the Invention and the accompanying drawing.